Shhh, Don’t Wake the Trees

Posted by
Brian at Tree In A Box
on June 02, 2016

We all need our sleep as most of us get cranky when we don’t
get enough sleep. Have you ever come across a cranky tree? Maybe they stole
your kite or Frisbee? As it turns out trees also enjoy a good night’s sleep.

A group of European scientist from the Vienna University of
Technology and the Finish Geodetic Institute and Hungary have used a high tech tool
to make an amazing discovery. The tool used was terrestrial LiDAR. Well
terrestrial means ground based and LiDAR is short for Light Detection and
Ranging. These ground based LiDAR units essentially send out thousands to
millions of laser pulses per second and measure the return distance of each
pulse to create a “point cloud” or 3D spatial scatter plot of millions of
points. These points can be accurate down the millimeter, depending on the
scanner and conditions used. Using these point clouds taken at different times,
you can then do a change analysis looking at differences in measurements over
time.

Most living organisms change their behaviors during day and
night. We sleep at night, some flowers close during the night and many other
organisms have not even been studied enough to know what their circadian
rhythms are. Scientists from all reaches of the globe have been studying day
night cycles and the effects on organisms for a long time. Early researchers
have recorded that some flowers still open and close in a dark room mimicking
their natural circadian rhythm. Most of the studies have been conducted in labs
using small plants, until this group of researchers decided to do some analysis
on fully grown trees using the same series of laser scanner.

What they found was that the whole tree droops at night,
which is observed by the position change in leaves and branches. According to Eetu Puttonen (Finnish Geospatial Research Institute), “The
changes are not too large, only up to 10 cm for trees with a height of about 5
meters, but they were systematic and well within the accuracy of our
instruments.”

True to the scientific method, the
experiment was done twice with two different trees to rule out effects of
weather and location. The first tree was surveyed in Finland and the other in
Austria. Both tests were done close to solar equinox, under calm conditions
with no wind or condensation. The leaves and branches were shown to droop
gradually, with the lowest position reached a couple of hours before sunrise.
In the morning, the trees returned to their original position within a few
hours. It is not yet clear whether they were “woken up” by the sun or by their
own internal rhythm.

So now that we know they sleep
there are so many other questions…. Like what happens if they get sleep
deprived? What happens if they get to much sleep? Do they sleep more in their
teenage years? Do seedlings keep up the old growth at night?